Water-dispersible polymer and coating composition containing the same

ABSTRACT

A water-dispersible polymer and a coating composition containing the water-dispersible polymer are disclosed. The water-dispersible polymer is prepared from: (a) an epoxy compound having about two epoxy groups, such as an epoxy resin, (b) a linking compound having (i) conjugated carbon-carbon double bonds or a carbon-carbon triple bond and (ii) a moiety capable of reacting with an epoxy group, such as sorbic acid, and (c) acrylic monomers, at least a portion of which are capable of rendering the polymer water dispersible, such as acrylic acid, wherein the epoxy portion (a) of the polymer is covalently linked to the polymerized acrylic portion (c) by linking compound (b). The coating composition contains the water-dispersible polymer, a fugitive base to solubilize the polymer, a curing agent, and a carrier containing water.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.08/603,885, filed Feb. 22, 1996, now U.S. Pat. No. 5,830,952.

FIELD OF THE INVENTION

The present invention relates to water-dispersible polymers and tocoating compositions for metal substrates containing thewater-dispersible polymers. The coating composition comprises awater-dispersible polymer, a fugitive base, a curing agent, and acarrier comprising water and a volatile organic solvent. Thewater-dispersible polymer is prepared from: (a) an epoxy compound havingabout two epoxy groups, (b) a linking compound having (i) conjugatedcarbon-carbon double bonds or a carbon-carbon triple bond and (ii) amoiety capable of reacting with an epoxy group, and (c) acrylicmonomers, wherein the epoxy portion (a) of the polymer is covalentlylinked to the polymerized acrylic portion (c) by the linking compound(b).

BACKGROUND OF THE INVENTION

It is well known that an aqueous solution in contact with an untreatedmetal substrate can result in corrosion of the untreated metalsubstrate. Therefore, a metal article, such as a metal container for awater-based product, like a food or beverage, is rendered corrosionresistant in order to retard or eliminate interactions between thewater-based product and the metal article. Conventionally, corrosionresistance is imparted to the metal article, or to a metal substrate ingeneral, by passivating the metal substrate, or by coating the metalsubstrate with a corrosion-inhibiting coating.

Investigators continually have sought improved coating compositions thatreduce or eliminate corrosion of a metal article and that do notadversely affect an aqueous product packaged in the metal article. Forexample, investigators have sought to improve the imperviousness of thecoating in order to prevent corrosion-causing ions, oxygen molecules,and water molecules from contacting and interacting with a metalsubstrate. Imperviousness can be improved by providing a thicker, moreflexible and more adhesive coating, but often, improving one particularadvantageous coating feature is achieved at the expense of anotheradvantageous coating feature.

In addition, practical considerations limit the thickness, adhesiveproperties and flexibility of a coating applied to a metal substrate.For example, thick coatings are expensive, require a longer cure time,can be esthetically unpleasing, and can adversely affect the process ofstamping and molding the coated metal substrate into a useful metalarticle. Similarly, the coating should be sufficiently flexible suchthat the continuity of the coating is not destroyed during stamping andmolding of the metal substrate into the desired shape of the metalarticle.

Investigators also have sought coatings that possess chemical resistancein addition to corrosion inhibition. A useful coating for the interiorof a metal container must be able to withstand the solvating propertiesof a product packaged in the metal container. If the coating does notpossess sufficient chemical resistance, components of the coating can beextracted into the packaged product and adversely affect the product.Even small amounts of extracted coating components can adversely affectsensitive products, like beer, by imparting an off-taste to the product.

Conventionally, organic solvent-based coating compositions were used toprovide cured coatings having excellent chemical resistance. Suchsolvent-based compositions include ingredients that are inherently waterinsoluble, and thereby effectively resist the solvating properties ofwater-based products packaged in the metal container. However, becauseof environmental and toxicological concerns, and in order to comply withincreasingly strict governmental regulations, an increasing number ofcoating compositions are water based. The water-based coatingcompositions include ingredients that are water soluble or waterdispersible, and, therefore, cured coatings resulting from water-basedcoating compositions often are more susceptible to the solvatingproperties of water.

Epoxy-based coatings and polyvinyl chloride-based coatings have beenused to coat the interior of metal containers for foods and beveragesbecause these coatings exhibit an acceptable combination of adhesion toa metal substrate, flexibility, chemical resistance, and corrosioninhibition. However, epoxy-based coatings and polyvinyl chloride-basedcoatings have serious disadvantages that investigators still areattempting to overcome.

For example, coatings based on polyvinyl chloride or relatedhalide-containing vinyl polymers, like polyvinylidene chloride, possessthe above-listed advantageous properties of chemical resistance andcorrosion inhibition, and are economical. However, curing a polyvinylchloride or related halide-containing vinyl polymer can generate toxicmonomers, such as vinyl chloride, a known carcinogen. In addition, thedisposal of a halide-containing vinyl polymer, such as by incineration,also can generate toxic monomers. The generated vinyl chloride therebyposes a potential danger to workers in metal can manufacturing plants,in food processing and packaging plants, and at disposal sites. Disposalof polyvinyl chloride and related polymers also can produce carcinogenicdioxins and environmentally harmful hydrochloric acid. Governmentregulators, therefore, are acting to eliminate the use of polyvinylchloride-based coating compositions that contact food, and therebyeliminate the environmental and health concerns associated withhalide-containing vinyl polymers.

To overcome these environmental concerns, epoxy-based coatingcompositions recently have been used to coat the interior of food andbeverage containers. However, epoxy-based coatings also possessdisadvantages. For example, epoxy-based coating compositions are moreexpensive than polyvinyl chloride-based coating compositions.

Various patents disclose waterborne coating compositions for metal cans.In general, prior patents disclose coating compositions includingwater-borne thermoset resins for use as can coatings. The thermosetresins can be formulated with a crosslinking agent to providecrosslinked films during cure, as demonstrated by the resistance of thecured coating to the effects of organic solvents such as methyl ethylketone. The cured thermoset resins often do not have sufficientflexibility for use as can coatings.

Recently, waterborne phenoxy resins were disclosed as useful in coatingsfor metal cans. These waterborne phenoxy resins are high molecularweight thermoplastic resins that are difficult to process and are tooexpensive for practical commercial use. In addition, because thesephenoxy resins are thermoplastic resins, cured coatings derivedtherefrom are not resistant to organic solvents, although the curedcoatings often provide sufficient barrier properties to water-basedcompositions for use as can coatings.

Investigators, therefore, have sought a waterborne coating compositionfor the interior of food and beverage containers that retains theadvantageous properties of adhesion, flexibility, chemical resistanceand corrosion inhibition, and that is economical and does not adverselyaffect the food and beverages packaged in the container.

Investigators prefer a thermosetting coating composition because suchcompositions are easier to handle and provide better chemical resistancethan thermoplastic coating compositions. A thermosetting coatingcomposition also requires a crosslinking agent, generally a phenolicresin, an aminoplast, or a similar resin, in order to provide a curedcoating having a sufficient molecular weight.

Prior investigators have studied waterborne epoxy resin-basedcompositions for application to metal substrates. Many of theseinvestigators sought epoxy resin-based aqueous compositions that providea sufficiently flexible cured coating such that the coated metalsubstrate can be deformed without destroying film continuity. Often,conventional epoxy resins provide a rigid cured film thereby making itdifficult to impossible to coat the metal substrate prior to deforming,i.e., shaping, the metal substrate into a metal article, like a metalcan. Coating a metal substrate prior to shaping the metal substrate is astandard industrial practice.

For example, Johnson et al. U.S. Pat. No. 4,954,553 discloses an aqueouscoating composition comprising a carboxyl-bearing phenoxy resin and aresin that is soft in comparison to the phenoxy resin, like a polyester.The carboxyl-bearing phenoxy resin is prepared by grafting ethylenicallyunsaturated monomers to the phenoxy resin. The coating compositionprovides flexible cured coatings. Fan U.S. Pat. Nos. 4,355,122 and4,374,875 disclose a water-borne phenolic composition wherein anethylenically unsaturated monomer including a carboxyl group is graftedonto a phenoxy resin by standard free radical polymerization techniques,then the carboxyl groups are neutralized by a base.

Chu et al. U.S. Pat. No. 4,446,258 discloses an aqueous coatingcomposition comprising: (1) the neutralized reaction product of an epoxyresin with a preformed addition polymer containing carboxyl groups, and(2) an acrylic or vinyl polymer, which is prepared either in situ oradded to the composition, and which is different from the preformedaddition polymer.

Evans et al. U.S. Pat. No. 4,212,781 discloses grafting an acrylicmonomer or monomer blend to an epoxy resin to provide a polymeric blendincluding unreacted epoxy resin, an acrylic resin and a graft polymer ofthe acrylic resin and epoxy resin. Steinmetz U.S. Pat. No. 4,302,373discloses a waterborne coating composition consisting essentially of theneutralized reaction product of a modified polyepoxide (e.g., an esteror ether) or a phenolic and a carboxyl-functional polymer.

Patel U.S. Pat. No. 4,963,602 discloses aqueous coating compositionsincluding an epoxy resin, an acrylic resin, a phenoxy resin, a novolacresin, and a resol resin. Wu U.S. Pat. Nos. 3,943,187 and 3,997,694disclose an organic solvent-based coating composition consistingessentially of a blend of an acrylic polymer having hard and softsegments and an epoxy resin. Salensky U.S. Pat. No. 4,638,038 disclosesmodified phenoxy resins wherein anhydrides or polycarboxylic acids aregrafted onto a phenoxy resin. Spencer U.S. Pat. No. 5,296,525 discloses(a) the reaction product of an epoxy resin with a monomer havingunsaturated groups, (b) wherein the reaction product of (a) then isreacted with a preformed carboxyl-functional polymer and a tertiaryamine, (c) followed by reacting the reaction product of (b) withunsaturated monomers in an emulsion polymerization.

Other patents that disclose epoxy resins admixed with acrylic resins, orhaving acrylic resins grafted thereon, include Matthews et al. U.S. Pat.No. 4,247,439; Evans et al. U.S. Pat. No. 4,308,185; Wu U.S. Pat. No.4,021,396; McCarty U.S. Pat. No. 4,444,923; Brown et al. U.S. Pat. No.4,585,813; and Ting et al. U.S. Pat. No. 4,480,058.

Publications disclosing a water-based coating compositions including anepoxy resin and an acrylic resin include:

J. T. K. Woo et al., "Synthesis and Characterization of Water-ReducibleGraft Epoxy Copolymers," J. Coat. Tech., 54 (1982), pp. 41-55; and

R. N. Johnson et al., "Water-Borne Phenoxy Resins Low VOC Coatings withExcellent Toughness, Flexibility and Adhesion," presented at theWater-Borne and Higher-Solid Coatings Symposium, Feb. 3-5, 1988 in NewOrleans, La.

The above-identified patents and publications disclose waterbornecoating compositions comprising an epoxy resin and an acrylic resin. Thepatents and publications do not disclose a waterborne coatingcomposition comprising a water-dispersible polymer comprising an epoxyresin covalently linked to an acrylic resin by a linking compound havingconjugated carbon-carbon double bonds or a triple bond.

The present coating compositions, after curing, demonstrate: (1)excellent flexibility; (2) excellent adhesion; and (3) excellentchemical resistance and corrosion inhibition.

SUMMARY OF THE INVENTION

The present invention is directed to waterborne coating compositionsthat, after curing, effectively inhibit corrosion of a metal substrate;do not adversely affect products packaged in a container having aninterior surface coated with the cured composition; and exhibitexcellent flexibility, chemical resistance and adhesion. The coatingcompositions effectively inhibit corrosion of ferrous and nonferrousmetal substrates when the composition is applied to a surface of themetal substrate, then cured for a sufficient time and at a sufficienttemperature to provide a crosslinked coating. A coating composition ofthe present invention can be used both on the interior and exterior ofcan ends and can bodies, and on metal closures for food containers.

A present coating composition overcomes disadvantages associated withprior epoxy resin-based compositions and comprises:

(a) a water-dispersible polymer prepared from

(i) an epoxy compound having about two epoxy groups, like an epoxyresin;

(ii) a linking compound having

(A) either conjugated carbon-carbon double bonds or a carbon-carbontriple bond, and

(B) a moiety capable of reacting with an epoxy group; and

(iii) acrylic monomers, at least a portion of which are capable ofrendering the polymer water dispersible, wherein the polymer has atleast one epoxy group and the epoxy portion (i) of the polymer iscovalently linked to the polymerized acrylic portion (iii) by linkingcompound (ii);

(b) a fugitive base, like a tertiary amine;

(c) a curing agent; and

(d) a carrier comprising water and a volatile organic solvent.

In particular, the present coating compositions comprise:

(a) about 5% to about 60%, by weight of nonvolatile material, of awater-dispersible polymer;

(b) a sufficient amount of a fugitive base to render thewater-dispersible polymer water dispersible; and

(c) about 0.5% to about 25%, by weight of nonvolatile material, of acuring agent, like a phenolic resin or an aminoplast.

The water-dispersible polymer incorporated into the coating compositionis prepared from (i) an epoxy compound, (ii) a linking compound havingan activated unsaturated carbon-carbon bond moiety and a moiety capableof reacting with an epoxy group, and (ii) acrylic monomers, at leastsome of which are capable of rendering the polymer water dispersible. Asused here and throughout the specification, the term "an activatedunsaturated carbon-carbon bond moiety" is defined as either conjugatedcarbon-carbon double bonds or a carbon-carbon triple bond.

The epoxy compound has about two epoxy groups, i.e., about 1.5 to about2.5 epoxy groups per molecule of epoxy compound, and an epoxy equivalentweight (EEW) of about 180 to about 20,000, and is present in an amountof about 5% to about 95% by weight of the polymer. The linking compoundhaving an activated unsaturated carbon-carbon bond moiety and a moietycapable of reacting with an epoxy group is present in a sufficientamount to react with at least about 1% (i.e., about 1% or more) and upto about 50% of the epoxy groups provided by the epoxy compound.Alternatively stated, the linking compound is present in an amount ofabout 0.1% to about 5% by weight of the epoxy compound, or about 0.003%to about 4% by weight of the water-dispersible polymer.

The polymerized acrylic monomers are present in an amount of about 5% toabout 95% by weight of the polymer. At least 5% by weight of thepolymerized acrylic monomers have a moiety, like a carboxylic acid oramide moiety, that render the polymer water dispersible. The polymercontains about 0.25% to about 20% by weight of polymerized acrylicmonomers having a moiety capable of imparting water dispersibility. Thepolymerized acrylic monomer portion of the polymer also can include 0%up to about 95% by weight of vinyl monomers, like styrene. Thepolymerized acrylic monomer portion of the polymer also can include 0%up to about 3% by weight of monomers having more than one vinyl group,like divinylbenzene.

The water-dispersible polymer, therefore, has the general structuralformula:

    E--L--A,

wherein E is the epoxy resin portion of the polymer, L is the linkingportion of the polymer, and A is the polymerized acrylic portion of thepolymer. The polymer is rendered water dispersible by adding a base,e.g., a fugitive base, to the polymer.

The epoxy portion of the water-dispersible polymer provides adhesion,and crosslinking capabilities for mar, chemical, and corrosionresistance. The acrylic portion of the water-dispersible polymerprovides flow, wetting, and hardness properties, and provides thehydrophilicity that is necessary to disperse the water-dispersiblepolymer in water. Linking the epoxy and acrylic portions providesenhanced flexibility and resistance properties to the water-dispersiblepolymer. The water-dispersible polymer, therefore, exhibits theexcellent flexibility and formability required in a can coating, andexhibits improved chemical resistance properties.

Components (a) through (c) of the coating composition are dispersed inan aqueous carrier such that a coating composition includes about 5% toabout 50%, and preferably about 10% to about 50% of nonvolatilecomponents, by weight of the total composition. Other optionalcomponents, such as a pigment, a filler, or an additive to enhancecomposition esthetics or performance, also can be included in thecomposition, and accordingly increase the weight percent of totalnonvolatile material in the composition to above about 60% by weight ofthe total coating composition. The carrier of the coating compositionalso includes a volatile organic solvent to assist in dispersing oremulsifying composition ingredients or to improve application of thecoating composition to a substrate. A coating composition typicallyincludes about 15% to about 35% by weight of a volatile organic solvent.

As used here and hereinafter, the term "coating composition" is definedas a coating composition including a water-dispersible polymer, afugitive base, a curing agent, and any other optional ingredientsdispersed in the carrier. The term "cured coating composition" isdefined as an adherent polymeric coating resulting from curing a coatingcomposition.

A coating composition, after application to a metal substrate, andsubsequent curing at a sufficient temperature for a sufficient time,provides an adherent layer of a cured coating composition thateffectively inhibits corrosion; exhibits excellent flexibility andadhesion to the metal substrate; and does not adversely affect aproduct, like a food or beverage, that contacts the cured coatingcomposition. Because of these advantageous properties, a cured coatingcomposition can be used to coat the interior of food and beveragecontainers and overcome the disadvantages associated with conventionalpolyvinyl chloride-based compositions and epoxy-based compositions. Acured coating composition comprises the water-dispersible polymer andthe curing agent essentially in the amounts these ingredients arepresent in the coating composition, expressed as nonvolatile material.The fugitive base is expelled, or removed, from a coating compositionduring the cure cycle.

In accordance with another important aspect of the present invention, acured coating composition demonstrates excellent flexibility, productresistance, and adhesion to a metal substrate compared to priorepoxy/acrylic resin-based coatings. The excellent adhesion of a curedcoating composition to a metal substrate improves thecorrosion-inhibiting properties of the coating composition. Theexcellent flexibility of a cured coating composition facilitatesprocessing of the coated metal substrate into a coated metal article,like in molding or stamping process steps, such that the cured coatingcomposition remains in continuous and intimate contact with the metalsubstrate. A cured coating composition also exhibits excellent chemicalresistance, is sufficiently hard to resist scratching, and does notadversely affect a food or beverage packaged in a container having aninterior surface coated with the cured coating composition.

In accordance with another important aspect of the present invention, acoating composition provides a cured coating composition that overcomesthe disadvantages of prior epoxy/acrylic-based coatings and ofconventional polyvinyl chloride-based coatings used to coat the interiorof containers for food and beverages. In addition, a present coatingcomposition can be used on both the interior and exterior of can bodiesand can ends, and on closures, thereby obviating the need for acontainer manufacturer to use multiple coating compositions.

These and other aspects and advantages of the present invention willbecome apparent from the following detailed description of the preferredembodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The coating compositions of the present invention, after curing, providecured coating compositions that effectively inhibit the corrosion ofmetal substrates, such as, but not limited to, aluminum, iron, steel andcopper. The cured coating compositions, after curing, also demonstrateexcellent adhesion to the metal substrate; excellent chemical resistanceand scratch resistance; and excellent flexibility.

In general, a coating composition of the present invention comprises:(a) a water-dispersible polymer, (b) a fugitive base, and (c) a curingagent in (d) a carrier comprising water and organic solvents. Inaddition, the present coating compositions can include optionalingredients, like lubricants, that improve the esthetics of thecomposition, that facilitate processing of the composition, or thatimprove a functional property of the composition. The individualcomposition ingredients are described in more detail below.

(a) The Water-Dispersible Polymer

The water-dispersible polymer is prepared from: (i) an epoxy compoundhaving about two epoxy groups, (ii) a linking compound having anactivated unsaturated carbon-carbon bond moiety and a moiety capable ofreacting with an epoxy group, and (iii) acrylic monomers, at least aportion of which are capable of rendering the polymer water dispersible.The linking compound (ii) provides a covalent link between the epoxycompound (i) and the polymerized acrylic monomers (iii).

In accordance with an important feature of the present invention, thewater-dispersible polymer is present in the coating composition in anamount of about 5% to about 60%, and preferably about 10% to about 50%,by weight of nonvolatile material.

As demonstrated hereafter, the epoxy portion of the water-dispersiblepolymer imparts adhesion properties, and chemical and mar resistance, toa cured coating composition. The acrylic portion of thewater-dispersible polymer provides the functionality necessary todisperse the polymer in water and also imparts flow, hardness, andwetting properties. Flexibility and chemical resistance of the curedcoating composition is improved over previous epoxy/acrylate-basedcompositions because a water-dispersible polymer having covalentlylinked epoxy and acrylic portions is present in the coating composition.The cured coating composition exhibits the advantageous properties of acombination of an epoxy resin and an acrylic resin, with the addedadvantage that the epoxy and acrylic portions of the polymer arecovalently linked.

The flexibility of a cured coating composition is an important featurebecause the coating composition then can be applied to a metalsubstrate, and cured, prior to shaping the metal substrate into a metalarticle, such as a can end, a can body, or a closure. The flexibilityimparted to a cured coating composition overcomes rigidity problemsassociated with prior epoxy-based compositions. The chemical and marresistance of the cured composition are important properties withrespect to resisting scratching of the cured coating composition duringmanufacture into a metal article and to resisting the corrosive effectsof materials packaged in the metal article.

The water-dispersible polymer is prepared from the epoxy compound, thelinking compound, and acrylic monomers. These components are reacted toprovide a water-dispersible polymer having an EEW of about 360 to about20,000, and preferably about 1,000 to about 12,000. Thewater-dispersible polymer has a weight average molecular weight (M_(w))of about 35,000 to about 75,000, and preferably about 45,000 to about65,000; and a number average molecular weight (M_(n)) of about 6,000 toabout 25,000, and preferably about 7,000 to about 16,000.

The individual components of the water-dispersible polymer are describedin more detail below.

(i) Epoxy Compound Having About Two Epoxy Groups

An epoxy compound having about two epoxy groups is present in an amountof about 5% to about 95%, and preferably from about 10% to about 90%, byweight of the water-dispersible polymer. To achieve the full advantageof the present invention, the epoxy compound is present in an amount ofabout 15% to about 85% by weight of the water-dispersible polymer.

During preparation of the water-dispersible polymer, a portion of theepoxy groups provided by the epoxy compound are consumed in a reactionwith the linking compound. However, as discussed hereafter, the epoxycompound, after modification by reaction with the linking compound,contains at least one epoxy group.

The epoxy compound contains an average of about 1.5 to about 2.5 epoxygroups per molecule of epoxy compound. If the average number of epoxygroups exceeds about 2.5, excessive crosslinking of the composition canresult in a cured coating that is too hard or brittle. The epoxycompound has an EEW of about 180 to about 20,000, and preferably about1,000 to about 12,000. To achieve the full advantage of the presentinvention, the epoxy compound has an EEW of about 2,000 to about 8,500.

The epoxy compound imparts chemical and mar resistance to the curedcoating composition. If the epoxy compound is present in an amount belowabout 5% by weight of the water-dispersible polymer, the cured coatingcomposition is brittle and can form cracks or lose adhesion duringmanufacture of a metal article. In addition, crosslinkable moieties arepresent in an insufficient amount to achieve proper cure of coating. Ifthe epoxy-containing compound is present in an amount above about 95% byweight of the water-dispersible polymer, the cured coating compositiondoes not have sufficient flow and wetting properties, and dispersion ofthe polymer in water is increasingly difficult. Within the above weightranges, the cured coating composition is sufficiently flexible to permitdeformation of a cured coating composition without forming cracks, andis sufficiently hard to exhibit excellent chemical and mar resistance.

The epoxy compounds having about two epoxy groups typically is a linearepoxy resin terminated at each molecular end of the resin with an epoxygroup. The epoxy compounds having about two epoxy groups, therefore,average about 1.5 to about 2.5 epoxy groups per molecule of epoxycompound.

The epoxy compound can be an aliphatic epoxy compound or an aromaticepoxy compound. The preferred epoxy compounds are aromatic, like epoxyresins based on the diglycidyl ether of bisphenol A. The epoxy compoundhas an EEW of about 180 to about 20,000, and preferably about 1,000 toabout 12,000. The epoxy compounds have a weight average molecular weight(M_(w)) of about 400 to about 50,000. An epoxy compound can be used inits commercially available form, or can be prepared by advancing a lowmolecular weight epoxy compound by standard methods well known to thoseskilled in the art, e.g., advancing an epoxy compound having an EEW ofabout 180 to about 500 with bisphenol A to produce an epoxy compoundhaving an EEW of about 1,000 to about 12,000.

Exemplary epoxy compounds include, but are not limited to, DER 664, DER667, DER 668, and DER 669, all available from Dow Chemical Co., Midland,Mich., and EPON 1004, EPON 1007, and EPON 1009, all available from ShellChemical Co., Houston, Tex. An exemplary low molecular weight epoxycompound that used in its commercial form, or can be advanced withbisphenol A, is EPON 828, available from Shell Chemical Co.

In general, suitable epoxy compounds are aliphatic-, cycoaliphatic-, oraromatic-based epoxy resins, such as, for example, epoxy resinsrepresented by structural formulae I and II: ##STR1## wherein each A is,independently, a divalent hydrocarbyl group having 1 to about 12,preferably 1 to about 6, and most preferably 1 to about 4, carbon atoms;each R is, independently, hydrogen or an alkyl group having 1 to about 3carbon atoms; each X is, independently, hydrogen, a hydrocarbyl orhydrocarbyloxy group having 1 to about 12, preferably 1 to about 6, andmost preferably 1 to about 4, carbon atoms, or a halogen atom,preferably chlorine or bromine; n is 0 or 1, and n' has an average valueof 0 to about 150, and preferably 0 to about 100.

In particular, the preferred epoxy resins are the (diglycidylether/bisphenol-A) resins, i.e., polyether diepoxides prepared by thepolymeric adduction of bisphenol-A (III) ##STR2## and the diglycidylether of bisphenol-A (IV). ##STR3## The diglycidyl ether can bepreformed by reacting two molecules of epichlorohydrin with one moleculeof the bisphenol-A in the presence of a base, such as sodium hydroxide.Preferably, however, this reaction is carried out in such a manner thatthe resulting diglycidyl ether molecules react in situ with bisphenolmolecules to produce the epoxy resin.

In this case, the epoxy resin is a mixture including polymeric speciescorresponding to different values of n' in the following idealizedformula V: ##STR4## wherein n' is a number from 0 to about 150.

In addition to bisphenol-A, useful epoxy resins can be prepared byadvancing a diglycidyl ether of a bisphenol listed below with anexemplary, but nonlimiting, bisphenol listed below: ##STR5##

Other epoxy resins that can be used as a component of thewater-dispersible polymer are prepared from the following startingepoxy-containing materials. These epoxy-containing materials are reactedwith bisphenol-A or another bisphenol to adjust the molecular weight ofthe epoxy compound to a sufficiently high range. ##STR6##

(ii) Linking Compound Having an Activated Unsaturated Carbon-Carbon BondMoiety and a Moiety Capable of Reacting with an Epoxy Group

The linking compound used to prepare a water-dispersible polymer has twofunctional groups and covalently links the epoxy portion of thewater-dispersible polymer to the polymerized acrylic monomer portion ofthe polymer. The linking compound is present in the water-dispersiblepolymer in an amount of about 0.003% to about 4%, and preferably about0.003% to about 2.5%, by weight of the water-dispersible polymer.

In accordance with another important feature of the present invention,the linking compound is present in a sufficient amount to react with atleast 1% and up to about 50% of the epoxy groups provided by the epoxycompound. Preferably, the linking compound is present in a sufficientamount to react with about 5% to about 40%, and most preferably about 5%to about 25%, of the epoxy groups provided by the epoxy compound.Accordingly, a reaction between the epoxy compound and the linkingcompound does not consume all the epoxy groups, and sufficient epoxygroups remain such that the water-dispersible polymer contains at leastone epoxy group.

As previously stated, the linking compound is a bifunctional monomer.One functionality is a moiety capable of reacting with an epoxy group.The second functionality is a moiety having an activated unsaturatedcarbon-carbon bond. As used herein, the term "activated unsaturatedcarbon-carbon bond" refers to a carbon-carbon triple bond, i.e., anacetylenic bond, or to conjugated carbon-carbon double bonds.

The linking compounds have the general structural formulae VI or VII##STR7## wherein R₁ is hydrogen, an aliphatic hydrocarbyl group, analiphatic cyclohydrocarbyl group, or an aromatic hydrocarbyl group; r isa numeral from 1 to 6; s is a numeral from 0 to 6; p is a numeral from 0to 18; and Y is a moiety capable of reacting with an epoxy group.Preferably, the linking compound has a maximum of twelve carbon atoms.

In particular, R₁ can be an aromatic hydrocarbyl group, like phenyl, ora substituted aromatic hydrocarbyl group, like a C₁ -C₁₀alkoxy-substituted phenyl, a halo-substituted phenyl, or a C₁ -C₁₈alkyl-substituted phenyl. As used herein, the term "halo" includesfluoro, chloro, bromo, and iodo. The R₁ group also can be an aliphatichydrocarbyl group or an aliphatic cyclohydrocarbyl group, eithersubstituted or unsubstituted. Nonlimiting examples of R₁ are hydrogen; aC₁ to C₁₈ alkyl group, and preferably a C_(1-C) ₁₀ alkyl group; a C₅ toC₇ cycloalkyl group; a phenyl-substituted C₁ -C₁₈ alkyl or C₅ -C₇cycloalkyl group; and a halo-substituted alkyl or cycloalkyl group. TheR₁ group also can be an unsaturated C₁ to C₁₈ aliphatic hydrocarbylgroup or an unsaturated C₅ to C₇ cycloaliphatic hydrocarbyl group, i.e.,the group contains one or more carbon-carbon double bonds orcarbon-carbon triple bonds. Such unsaturated aliphatic hydrocarbyl andcyclohydrocarbyl groups can be substituted or unsubstituted. Anysubstituent groups on R₁ are sufficiently nonreactive such that thesubstituents do not interfere in the preparation of the modified epoxycompound or the water-dispersible polymer. To achieve the full advantageof the present invention, R₁ is hydrogen, a C₁ -C₄ alkyl group, a C₅ -C₇cycloalkyl group, or phenyl.

The identity of the Y group is not limited, except that the Y group iscapable of reacting with an epoxy group. Therefore, the Y group can be,but is not limited to, carboxyl (--CO₂ H), amido (--CON(R₂)₂), amino(--N(R₂)₂), hydroxyl (--OH), or mercapto (--SR₃), wherein R₂ groups are,independently, hydrogen, C₁ -C₄ alkyl, or phenyl, and R₃ is hydrogen, C₁-C₄ alkyl, or phenyl.

Specific linking compounds include, but are not limited to, sorbic acid,sorbic alcohol, dicyclopentadiene acids, conjugated unsaturated fattyacids (e.g., eleostearic acid), 3-pentyn-1-ol, 2-pentyn-1-ol,4-pentynoic acid, 4-pentyn-1-ol, 4-pentyn-2-ol, 1-pentyn-3-ol,heptacose-10,12-diynoic acid, heptadeca-2,4-diynoic acid,heneicosa-2,4-diynoic acid, 2-heptynoic acid, 2-hexynoic acid,nonacosa-10,12-diynoic acid, nonadeca-1,4-diynoic acid, 2-nonynoic acid,pentadeca-2,4-diynoic acid, pentacosa-10,12-diynoic acid,phenylpropiolic acid, propiolic acid, tetrolic acid,tricosa-10,12-diynoic acid, 10-undecynoic acid, 1-butyn-3-ol,2-butyn-1-ol, 3-butyn-1-ol, 2-decyn-1-ol, 3-decyn-1-ol,3,6-dimethyl-1-heptyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol,3,4-dimethyl-1-pentyn-3-ol, 3-ethyl-1-heptyn-3-ol, 4-ethyl-1-hexyn-3-ol,3-ethyl-5-methyl-1-heptyn-3-ol, 4-ethyl-1-octyn-3-ol,3-ethyl-1-pentyn-3-ol, 1-ethynyl-1-cyclohexanol, 1-heptyn-3-ol,2-heptyn-1-ol, 3-heptyn-1-ol, 4-heptyn-2-ol, 5-heptyn-3-ol,1-hexyn-3-ol, 2-hexyn-1-ol, 3-hexyn-1-ol, 4-hexyn-2-ol, 5-hexyn-1-ol,5-hexyn-3-ol, 3-methyl-1-butyn-3-ol, 5-methyl-1-hexyn-3-ol,3-methyl-1-pentyn-3-ol, 3-nonyn-1-ol, 1-octyn-3-ol, 3-octyn-1-ol,1-phenyl-2-propyn-1-ol, 2-propyn-1-ol, 10-undecyn-1-ol,3-aminophenylacetylene, propargylamine, and mixtures thereof. Apreferred linking compound is sorbic acid, having the structure (VIII).

    CH.sub.3 --CH═CH--CH═CH--CO.sub.2 H                (VIII)

(iii) Acrylic Monomers

The acrylic monomers, after polymerization, are present in an amount ofabout 5% to about 95%, and preferably about 10% to about 90%, by weightof the water-dispersible polymer. To achieve the full advantage of thepresent invention, the polymerized acrylic monomers are present in anamount of about 15% to about 85%, by weight of the water-dispersiblepolymer.

The acrylic monomers are polymerized in a free radical polymerizationreaction, in the presence of the linking compound, to covalently bondthe acrylic portion of the water-dispersible polymer to the linkingcompound through the activated unsaturated carbon-carbon bond moiety.Preferably, the acrylic monomers are polymerized in the presence of thelinking compound after the linking compound has been covalently bound tothe epoxy compound.

In accordance with an important feature of the present invention, atleast a portion of the acrylic monomers are capable of rendering thepolymer dispersible in water. These monomers are defined as monomersthat yield either water-soluble homopolymers or homopolymers that arerendered water soluble by neutralization with a base. The acrylicmonomers can include 0% up to about 95%, by total weight of monomers, ofvinyl monomers. To avoid excessive branching, the amount of polyvinylmonomers is 0% to about 3% by total weight of monomers.

The acrylic monomer typically comprises an α,β-unsaturated carboxylicacid. The α-β unsaturated carboxylic acid renders the polymer waterdispersible after neutralization with a base. Suitable α,β-unsaturatedcarboxylic acid monomers include, for example, acrylic acid, methacrylicacid, crotonic acid, itaconic acid, maleic acid, mesaconic acid,citraconic acid, sorbic acid, fumaric acid, and mixtures thereof. Theacrylic monomer also can include acrylamide or methacrylamide which canrender the polymer water dispersible.

The α,β-unsaturated carboxylic acid conventionally is copolymerized witha vinyl or an acrylic monomer, like styrene or an acrylic acid ester.Polymerizable vinyl and acrylic monomers suitable for copolymerizationwith an α,β-unsaturated carboxylic acid include, for example, aromaticand aliphatic compounds including vinyl moieties and esters and amidesof α,β-unsaturated carboxylic acids. Nonlimiting examples of suitablevinyl and acrylic monomers include styrene and halostyrenes; isoprene;conjugated butadiene; α-methylstyrene; vinyl toluene; vinyl naphthalene;the methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isoamyl,hexyl, ethylhexyl, lauryl, and other C₄ -C₁₂ alkyl acrylates,methacrylates and crotonates; dimethyl maleate, dibutyl fumarate andsimilar diesters of α,β-unsaturated dicarboxylic acids; and mixturesthereof. Other suitable polymerizable vinyl monomers include vinylchloride, acrylonitrile, methacrylonitrile, vinyl acetate, vinylpropionate, vinyl stearate, isobutoxymethyl acrylamide, and the like.

The preferred acrylic monomers are methyl acrylate, methyl methacrylate,ethyl acrylate, butyl acrylate, acrylic acid, methacrylic acid, andmixtures thereof. A preferred vinyl monomer is styrene. The mostpreferred acrylic and vinyl monomers are styrene, methacrylic acid,acrylic acid, and mixtures thereof.

The acrylic monomers are polymerized and covalently bonded to thelinking compound by subjecting the acrylic monomers and the linkingcompound to free radical polymerization conditions known to personsskilled in the art. Therefore, the acrylic monomers are polymerized andcovalently bonded to the linking compound in the presence of a freeradical initiator. Useful free radical initiators include, but are notlimited to, redox initiators, peroxide-type catalysts, like, forexample, cumene hydroperoxide, or azo compounds, like, for example,azobisisobutyrontrile.

In general, any free radical initiator can be used in preparing thewater-dispersible polymer. One commonly used, and preferred, freeradical initiator is potassium persulfate. In addition to potassiumpersulfate, other useful free radical polymerization catalysts include,but are not limited to, redox initiators, such as a sulfite or bisulfiteof an alkali metal, ammonium sulfite, ammonium metabisulfate, ammoniumbisulfite, a persulfate of an alkali metal or ammonium persulfate; aperoxy compound, such as a peroxide or a peroxy acid, like t-butylhydroperoxide, di-t-butyl hydroperoxide, benzoyl hydroperoxide, t-butylperoxide, lauroyl peroxide, methyl ethyl ketone peroxide, chlorobenzoylperoxide, t-butyl perbenzoate, t-butyl peroxy isopropyl carbonate, andperoxy-3,3,5-trimethylcyclohexane, or a mixture thereof. Also useful arefree radical thermal initiators such as azobisisobutyronitrile;4-t-butylazo-4'-cyanovaleric acid; 4,4'-azobis(4-cyanovaleric acid);2,2'-azobis(2-amidinopropane)dihydrochloride;2,2'-azobis(2,4-dimethylvaleronitrile); dimethyl 2,2'-azobisisobutyrate;2,2'-azodimethyl bis(2,4-dimethyl-valeronitrile);(1-phenylethyl)azodiphenylmethane; 2,2'-azobis(2-methylbutyronitrile);1,11-azobis(1-cyclohexanecarbonitrile);2-(carbamoylazo)-isobutyronitrile;2,2'-azobis(2,4,4-trimethylpenta-2-phenylazo-2,4-dimethyl-4-methoxy)valeronitrile;2,2'-azobis(2-methylpropane);2,2'-azobis(N,N'dimethyleneisobutyramidine)dihydrochloride;4,4'-azobis(4-cyanopentanoic acid); 2,2'-azobis(2-methyl-N-1,1-bis-hydroxymethyl)-2-hydroxyethyl! propionamide);2,2'-azobis(2-methyl-N- 1,1-bis(hydroxymethyl)-ethyl!propionamide);2,2'-azobis 2-methyl-N(2-hydroxyethyl)propionamide!;2,2'-azobis(isobutyramide) dihydrate, and the like. These types ofinitiators, redox, peroxy, and thermal, can be used singly or in asuitable mixture.

The water-dispersible resin is prepared either by reacting the linkingcompound with an epoxy compound or by advancing a low molecular weightepoxy compound to a desired EEW while simultaneously reacting theadvanced epoxy resin with the linking compound, followed by polymerizingthe acrylic monomer in the presence of the linking compound bonded tothe epoxy compound. The preferred method simultaneously advances a lowmolecular weight epoxy compound while reacting the advanced epoxycompound with the linking compound.

For purposes of illustrating the preparation of a water-dispersiblepolymer, the following experiments and reactions were performed.

First, the ability of a linking compound to covalently bond to an epoxygroup without disrupting the activated unsaturated carbon-carbon bondmoiety of the linking compound was demonstrated by reacting1,2-epoxy-3-phenoxypropane (IX) with sorbic acid (VIII) to providecompound (X). ##STR8##

In particular, compound (X) was prepared by admixing 74.0 gram (g) (0.49equivalents) of compound IX, 55.3 g (0.49 equivalents) of sorbic acid,0.006 g (500 ppm) tetraethylammonium bromide (TEAB), and 20 g methylethyl ketone in a reaction flask to form a reaction mixture. The initialacid number of the reaction mixture was about 184.1. A blanket ofnitrogen gas (N₂) was applied over the reaction mixture, then thereaction mixture was heated to 200° F., and held at 200° F. until theacid number was reduced to less than one. During the reaction, a secondportion of 0.06 g TEAB as added to the heated reaction mixture. Afterthe acid number dropped below one, the reaction mixture was cooled, andthe methyl ethyl ketone was stripped from the reaction mixture toprovide compound (X). The structure of compound (X) was confirmed bynuclear magnetic resonance (NMR) spectroscopy.

In experiments wherein sorbic acid was reacted with an advanced epoxyresin (e.g., EEW of about 1,000), the reaction mixture often was tooviscous to completely dissolve the advanced epoxy resin and allow ahomogeneous reaction with the sorbic acid. To overcome this problem,sorbic acid (VIII) and bisphenol-A (III) were admixed with a lowmolecular weight epoxy compound, and allowed to react simultaneouslywith the epoxy compound. The structure of the resulting epoxy-sorbatepolymer was confirmed by NMR spectroscopy. The conjugated diene portionof sorbic acid was not effected during the reaction. Thesorbate-modified epoxy compound, therefore, has the structure (XI).##STR9## wherein t is 0 to about about 70. The sorbate-modified epoxycompound (XI), therefore, has epoxy groups available for reaction with acrosslinking agent and an activated unsaturated carbon-carbon bondmoiety available for reaction with the acrylic monomers.

In other embodiments, the epoxy ring remaining in sorbate-modified epoxycompound (XI) is opened prior to reacting the sorbate-modified epoxycompound with the acrylic monomers. For example, the epoxy ring incompound (XI) can be hydrolyzed to provide the corresponding α-glycolcompound, wherein the epoxy ring at the terminal end of thesorbate-modified epoxy compound is converted to structure (XII).##STR10##

Similarly, the epoxy ring of compound (XI) can be opened with a nitrogencompound having the structure (R₄)₂ NH, wherein the R₄ groups are,independently, hydrogen, phenyl, or an alkyl or hydroxyalkyl grouphaving one to six carbon atoms. Examples of such nitrogen compounds areammonia, a primary amine, or a secondary amine. Opening the epoxy ringwith a nitrogen compound provides an α-aminoalcohol at a terminal end ofthe modified epoxy compound (XI).

In addition, the epoxy ring of a modified epoxy compound can be openedwith a hydroxyl-containing compound having the structure R₅ OH, whereinR₅ is an alkyl group or a hydroxyalkyl group having one to six carbonatoms, or R₅ is phenyl. Opening the epoxy ring with an alcohol providesan α-hydroxy ether at a terminal end of the modified epoxy compound.

Furthermore, the epoxy ring of the modified epoxy compound can be openedwith phosphoric acid having the structure (XIII), ##STR11## wherein theR₆ groups are, independently, hydrogen, an alkyl group or a hydroxyalkylgroup having one to six carbon atoms, or phenyl. Opening the epoxy ringwith a phosphoric acid of structure (XIII) provides an α-hydroxyphosphate ester having the structure (XIV) ##STR12## at the terminal endof the modified epoxy compound (XI).

To demonstrate that the linking compound copolymerizes with the acrylicmonomers, sorbic acid was reacted with acrylic monomers and vinylmonomers under free radical polymerization conditions. The conjugateddiene moiety of sorbic acid was not observed in the resulting polymer.In particular, the following example demonstrates the copolymerizationof sorbic acid, acrylic monomers, and vinyl monomers.

    ______________________________________    Ingredient             Amount (wt)    ______________________________________    (a)     Butyl Cellosolve   316    g    (b)     n-Butyl Alcohol    96     g    (c)     Styrene            5.1    g    (d)     Ethyl Acrylate     113.4  g    (e)     Methyl Methacrylate                               33.9   g    (f)     Acrylic Acid       21.3   g    (g)     Methacrylic Acid   25.5   g    (h)     Sorbic Acid        3      g    (i)     2,2'-Azobisisobutyronitrile                               3      g    (j)     Butyl Cellosolve   50     g    (k)     2,2'-Azobisisobutyronitrile                               1.3    g    (l)     2,2'-Azobisisobutyronitrile                               1.3    g    (m)     2,2'-Azobisisobutyronitrile                               1.3    g    ______________________________________

Ingredients (a) and (b) were charged into a reaction flask and heated to230° F. Ingredients (c) through (i) were premixed, then added dropwiseto the heated mixture of (a) and (b) over a 90-minute period, withagitation and while maintaining a temperature of 230°-235° F. Residualamounts of the monomer premix (c)-(i) were washed into the reactionflash with ingredient (j). The resulting reaction mixture was held at230° F. for 30 minutes, then ingredient (k) was added. After another30-minute hold at 230° F., ingredient (l) was added. After a third30-minute hold at 230° F., ingredient (m) was added. The reactionmixture then was held at 230° F. for an additional 60 minutes, thenallowed to cool.

The solvents were evaporated from the reaction mixture, and theresulting copolymer was assayed by NMR for the presence of the sorbicacid diene moiety. No evidence of a diene moiety was observed.

As illustrated hereafter, a sorbate-modified epoxy compound ofstructural formula (XI) was reacted with acrylic and vinyl monomers toprovide a water-dispersible polymer. The resulting water-dispersiblepolymer had the structure:

    E--L--A,

wherein E is the epoxy portion of the polymer, A is the acrylic portion,and L is the linking portion which covalently links E to A.

(b) The Fugitive Base

The water-dispersible polymer contains a sufficient amount of acrylicmonomers capable of rendering the polymer dispersible in water. Theseacrylic monomers typically are α,β-unsaturated carboxylic acids andthese monomers render the polymer water dispersible by neutralizing thecarboxylic acid moiety with a fugitive base.

A fugitive base is included in a sufficient amount such that about 20%to about 100% of the carboxylic acid groups of the acrylic portion ofthe water-dispersible monomer are neutralized. An excess amount offugitive base does not adversely affect the coating composition, but theexcess amount of fugitive base provides no advantages and, therefore, iswasted. A fugitive base preferably is present in an amount sufficient toneutralize at least about 35% to about 75% of the carboxylic acid groupspresent in a water-borne coating composition. The precise amount offugitive base added to the composition is determined from the acidnumber of the water-dispersible polymer and from the basicity offugitive base.

A fugitive base is a relatively volatile compound that is expelled froma coating composition during cure. Accordingly, a coating composition,during cure, reverts to a more water insoluble form and, therefore,provides a cured coating composition that exhibits excellent chemicalresistance and excellent blush resistance.

A fugitive base usually is a primary, secondary or tertiary amine,either aromatic or aliphatic, or a primary, secondary or tertiaryalkanolamine, or ammonium, an alkylammonium hydroxide, or anarylammonium hydroxide, or mixtures thereof. Nonlimiting examples of afugitive base include ammonium hydroxide, a tetraalkylammoniumhydroxide, wherein an alkyl group has one to about 4 carbon atoms (e.g.,tetramethylammonium hydroxide), monoethanolamine, dimethylamine,methyldiethanolamine, benzylamine, diisopropylamine, methylethanolamine,butylamine, piperazine, dimethylethanolamine, diethylethanolamine,diethanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine,triethylamine, 2-dimethylamine-2-methyl-1-propanol, diisopropanolamine,trimethylamine, N-methylpiperidine, 2-amino-2-methyl-1-propanol,piperidine, pyridine, dimethylaniline, and similar amines andalkanolamines, and mixtures thereof.

(c) The Curing Agent

A coating composition of the present invention also includes a curingagent, such as a phenolic resin or an aminoplast. The coatingcomposition contains about 0.5% to about 25%, and preferably about it toabout 20%, by weight of nonvolatile material of the curing agent. Toachieve the full advantage of the present invention, the coatingcomposition contains about it to about 10%, by weight, of a curingagent.

The curing agent can be a phenolic resin, an aminoplast, a carbodiimide,or a similar curing agent. The phenolic resin is a condensation productresulting from a reaction between a phenol and formaldehyde, and has alow weight average molecular weight of about 800 to about 8,000, andpreferably about 1,200 to about 5,000. Phenol or essentially any othercompound including a hydroxyphenyl moiety can be used as the phenolcomponent of the phenolic resin. Nonlimiting examples of suitable phenolcompounds include phenol, cresylic acid and bisphenol A. Bisphenol A isthe preferred phenol component of the phenolic resin.

Similarly, an aminoplast can be used as the curing agent. An aminoplastgenerally is a low molecular weight partially or fully alkylatedcondensation product, like urea-formaldehyde, melamine-formaldehyde, andbenzoguanamine-formaldehyde resins.

Commercially available aminoplasts include, for example, CYMEL 301,CYMEL 303, CYMEL 370, and CYMEL 373, all being melamine-based andcommercially available from American Cyanamid, Stamford, Conn., e.g.,CYMEL 301 is hexamethoxymethyl melamine.

Other examples of aminoplast resins are of the type produced by thereaction of aldehyde and formoguanamine, ammeline,2-chloro-4,6-diamine-1,3,5'triazine;2-phenyl-p-oxy-4,6-diamino-1,3,5-triazine; and2,4,6-triethyl-triamino-1,3,5-triazine. The mono-, di, or triarylmelamines, for instance, 2,4,6-triphenyltriamine-1,3,5-triazine, arepreferred. Other aldehydes used to react with the amino compound to formthe resinous material are crotonic aldehyde, acrolein, or compoundswhich generate aldehydes, such as hexamethylene-tetramine, paraldehyde,and the like.

(d) The Carrier

The carrier of a present coating composition is water based, but alsocan include a volatile organic solvent. In general, the volatile organicsolvents included in the coating composition have sufficient volatilityto evaporate essentially entirely from the coating composition duringthe curing process, such as during heating at about 350° F. to about500° F. for about 6 seconds to about 15 minutes.

The volatile organic solvents are included as a portion of the carrierto help dissolve, disperse and emulsify composition ingredients, andthereby provide a more stable composition. The volatile organic solventsalso are included to improve the physical properties of the composition,like surface tension, flow out during the bake and viscosity, andthereby provide a composition that is easier to apply and that providesa more uniform cured coating. The volatile organic solvents improve theflow properties of a coating composition and facilitates spraying of acoating composition.

Numerous volatile organic solvents can be included in a present coatingcomposition. Suitable volatile organic solvents have a sufficiently lowvapor pressure to resist evaporation during storage and a sufficientlyhigh vapor pressure to be evaporated from the coating composition duringcure. Exemplary, nonlimiting volatile organic solvents include, but arenot limited to, the methyl, ethyl, propyl, butyl, hexyl or phenyl etherof ethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol or dipropylene glycol; ethylene glycol methyl ether acetate;ethylene glycol ethyl ether acetate; ethylene glycol butyl etheracetate; diethylene glycol ethyl ether acetate; diethylene glycol butylether acetate; propylene glycol methyl ether acetate; dipropylene glycolmethyl ether acetate; n-butanol; hexyl alcohol; hexyl acetate; methyln-amyl ketone; butylene glycol; propylene glycol; diisobutyl ketone;methyl propyl ketone; methyl ethyl ketone; methyl isobutyl ketone;2-ethoxyethyl acetate; t-butyl alcohol; amyl alcohol; 2-ethylhexylalcohol; cyclohexanol; isopropyl alcohol; and similar organic solvents,and mixtures thereof.

A preferred volatile organic solvent is n- butanol because coatingcomposition components are easily dispersed in n-butanol. Anotherpreferred volatile organic solvent is ethylene glycol monobutyl ether,i.e., butyl cellosolve.

The carrier also can include a relatively low amount of a nonpolarorganic solvent, such as up to about 10% by weight of the carrier,without adversely affecting a coating composition, either prior to orafter curing. Exemplary nonpolar organic solvents include a chlorinatedhydrocarbon, an aliphatic hydrocarbon, or an aromatic hydrocarbon, liketoluene, ethylbenzene, benzene, xylene, mineral spirits, kerosene,naphtha, heptane, hexane, and combinations thereof.

The amount of carrier included in the coating composition is limitedonly by the desired, or necessary, Theological properties of a coatingcomposition. Usually, a sufficient amount of carrier is included in acoating composition to provide a composition that can be processedeasily, that can be applied to a metal substrate easily and uniformly,and that is sufficiently evaporated from a coating composition duringcure within the desired cure time.

A carrier, therefore, is included in the composition in a sufficientamount to provide a coating composition including about 5% to about 60%,and preferably about 10% to about 50%, by weight of the nonvolatilematerial. To achieve the full advantage of the present invention, awaterborne coating composition includes about 15% to about 45% by weightof the nonvolatile material. The addition of optional fillers canincrease the amount of nonvolatile material above about 60%.

Therefore, essentially any carrier comprising a major portion of waterand a minor portion of volatile organic solvents is useful in thepresent coating composition as long as the carrier adequately disperses,emulsifies and/or solubilizes the composition components; is inert withrespect to interacting with composition components and thereby adverselyaffecting the stability of the coating composition or the ability of thecoating composition to effectively cure; and evaporates quickly,essentially entirely and relatively rapidly to provide a cured coatingcomposition that inhibits the corrosion of a metal substrate, that doesnot adversely affect a food or beverage that contacts the cured coatingcomposition, and that demonstrates sufficient physical properties, likeadhesion and flexibility, for use as a coating on the interior orexterior of a container or a closure.

(e) Other Optional Ingredients

A coating composition of the present invention also can include otheroptional ingredients that do not adversely affect the coatingcomposition or a cured coating composition resulting therefrom. Suchoptional ingredients are known in the art, and are included in a coatingcomposition to enhance composition esthetics; to facilitatemanufacturing, processing, handling, and application of the composition;and to further improve a particular functional property of a coatingcomposition or a cured coating composition resulting therefrom.

Such optional ingredients include, for example, dyes, pigments,extenders, fillers, additional anticorrosion agents, flow controlagents, thixotropic agents, dispersing agents, antioxidants, adhesionpromoters light stabilizers, and mixtures thereof. A nonionic or ananionic surfactant is included in a coating composition to improve flowproperties. A wax emulsion and/or dispersion of a synthetic lubricant isincluded to improve the slip properties of a cured coating composition.Each optional ingredient is included in a sufficient amount to serve itsintended purpose, but not in such an amount to adversely affect acoating composition or a cured coating composition resulting therefrom.

A coating composition of the present invention is prepared by firstpreparing the water-dispersible polymer. The water-dispersible polymerpreferably is prepared by simultaneously advancing the epoxy compoundand reacting the epoxy compound with the linking compound. The resultingmodified epoxy compound is reacted with acrylic monomers under freeradical polymerization conditions to provide the water-dispersiblepolymer.

The water-dispersible polymer then is admixed with the fugitive base,curing agent, and carrier, i.e., water and volatile organic solvent. Thecarrier is present in a sufficient amount to adjust the amount ofnonvolatile material in the coating composition to a predeterminedlevel. Optional ingredients can be added to the coating compositioneither prior to or after the addition of the carrier.

To demonstrate a coating composition of the present invention, thefollowing Examples and Comparative Examples were prepared, then appliedto a metal substrate, and finally cured to provide a coated metalsubstrate. The coated metal substrates then were tested, comparatively,for use as a food or beverage container. The cured coatings were testedfor an ability to inhibit corrosion of a metal substrate; for adhesionto the metal substrate; for chemical resistance; for flexibility; andfor scratch and mar resistance. A composition of the present inventionwas compared to a commercial vinyl organosol composition (i.e.,Comparative Example 1) that is widely used in coating metal substratesfor food and beverage applications.

    ______________________________________    Comparative Example 1    Commercial Vinyl Organosol Composition                     %         % (by    Ingredient       (by weight)                               weight NVM.sup.1)    ______________________________________    Xylene           29.45     --    Diisobutyl Ketone                     13.77     --    Diacetone Alcohol                     20.90     --    Solution Vinyl .sup.2                     11.61     34.32    Phenolic Resin .sup.3                     2.02      2.99    Epoxy Resin .sup.4                     1.01      2.99    Lubricant .sup.5 1.31      0.77    Vinyl Cloride Dispersion                     19.93     58.92    Resin.sup.6    ______________________________________     .sup.1  NVM is nonvolatile material;     .sup.2  UCAR Solution Vinyl VMCC, available as a 100% active material,     from Union Carbide Corp., Danbury, CT;     .sup.3  50% nonvolatile material;     .sup.4  EPON 828, available as a 100% active material, from Shell Chemica     Co., Houston, TX;     .sup.5  POLYSPERSE ®, 20% active material; and     .sup.6 OXY 1730, available as a 100% active material, from Occidental     Chemical Co., Houston, TX.

The composition of Comparative Example 1 contains about 33.8%nonvolatile material.

    ______________________________________    EXAMPLE 1                              % (by    Ingredient     % (by weight)                              weight NVM.sup.1)    ______________________________________    Water-Dispersible                   91.46      97.0    Polymer/Fugitive    Base Solution.sup.7    Curing Agent .sup.8                   1.52       2.3    Lubricant .sup.9                   0.92       0.7    N-Butyl Alcohol                   1.22    Deionized Water                   4.88    ______________________________________     .sup.7 Aqueous solution of waterdispersible polymer solubilized with     dimethylethanolamine, 35% solids content, see Example 2;     .sup.8  Phenolic resin, based on phenol and paraformaldehyde, 50% active;     and     .sup.9  MICHEM 160, Michelman Chemical Inc., Cincinnati, OH, a 25% active     emulsion of carnauba wax.

The composition of Example 1 is a coating composition of the presentinvention containing about 33% nonvolatile material. The composition ofExample 1 is prepared by simply admixing composition ingredients untilhomogeneous. The composition of Example 1 is based on thewater-dispersible polymer prepared as set forth below in Example 2.

EXAMPLE 2 Water-Dispersible Polymer/Fugitive Base Solution

An epoxy compound, i.e., EPON 828, a diglycidylether of bisphenol-A,(EEW 187, 180 pounds) was added to a nitrogen-blanketed reactor fittedwith a reflux condenser. The epoxy compound was heated to about 170° F.to about 175° F., then a sufficient amount of bisphenol-A was added tothe heated epoxy compound to provide an epoxy resin of EEW of about 3000(e.g., about 99 pounds). In addition, 464 grams (g) of sorbic acid and77 g of a phosphonium salt catalyst (i.e., SHELL Catalyst 1201,available from Shell Chemical Co., Houston, Tex.) were added to thereactor.

The resulting mixture was heated to 240° F. while maintaining a nitrogenblanket. After reaching 240° F., the mixture was allowed to cool to 100°F. An exothermic reaction raised the temperature to 270° F., and thetemperature then was allowed to raise at the rate of about one to aboutone and one-half Fahrenheit degrees per minute by cooling the mixtureuntil the temperature reached about 350° F. (peak temperature was about365° F.). After the exotherm subsided, the mixture was held at about350° F. to about 360° F., by heating, for about one hour. When the epoxyresin attained an EEW of greater than about 3000, butyl cellosolve (176pounds) was added to the mixture, and the mixture was allowed to cool toabout 250° F.

Then, n-butyl alcohol (32.8 pounds) was added to the mixture, and theresulting mixture was further cooled to 230° F. A premix of styrene (790g), ethyl acrylate (38.7 pounds), methyl methacrylate (11.6 pounds),acrylic acid (3,299 g), and methacrylic acid (3,950 g), and having anacid number of about 166, was prepared. Azobisisobutyronitrile initiator(464 g) was added to the monomer premix, then the resulting acrylicmonomer/initiator mixture was added to the reactor over a 90-minute timeperiod, while maintaining a temperature of about 230° F. Residualamounts of acrylic monomers were flushed into the reaction vessel with14.4 pounds of butyl cellosolve and held at about 230° F. for anadditional 30 minutes.

Next, a premix of 201 g of azobisisobutyronitrile and 402 g of butylcellosolve was added to the reactor, and the resulting mixture was heldfor an additional 30 minutes at about 230° F. This procedure wasrepeated two additional times to ensure that the acrylic monomers werepolymerized.

The contents of the reactor then were cooled to about 220° F., followedby the addition of 4090 g of deionized water. The contents of thereactor were cooled to 212° F., then a premix of water (4090 g) anddimethylethanolamine (4090 g) was added to the reactor. After a10-minute hold, heated deionized water (262 pounds, 200° F.) was addedto the reactor over a one-hour time period. The reaction product wasallowed to cool to about 195° F. to about 200° F. during the wateraddition. Next, deionized water (135 pounds) was quickly added to coolthe reaction product to about 105° F. The reaction product then wasadjusted to the desired solids content by the addition of deionizedwater.

The polymer solution of Example 2 had a solids content of about 35%, byweight; a pH of about 7.25; a viscosity of 350 cps (centipoise) measuredon a #3 spindle at 25° C. and 20 rpm; an acid number on solids of about32.5, and a base number on solids of about 16.2. The water-dispersiblepolymer/fugitive base solution of Example 2 was used as the majorcomponent of the composition of Example 1.

The composition of Example 1 was applied to both sides of an aluminumsubstrate at a rate to provide about 5.2 to about 7 milligrams persquare inch (msi) interior dry film weight and about 2.3 to about 2.8msi exterior dry film weight. The composition of Example 1 was appliedat a rate of about 150 feet per minute, and was cured at about 450° F.for about 11 seconds. The composition of Example 1 was easy to apply,exhibiting excellent flow, no foaming, no skinning, no significantsolvent loss, and no apparent rise in viscosity after two hours. Thecured coating composition exhibited excellent gloss.

The composition of Example 1 was compared to the composition ofComparative Example 2. Comparative Example 1 was used as a control. Thecomposition of Comparative Example 2 was similar to the composition ofExample 1, except sorbic acid was omitted from the composition ofExample 2. The composition of Comparative Example 2, therefore, does notinclude a linking compound to covalently bond the epoxy portion of thepolymer to the polymerized acrylic portion of the polymer.

In summary, Comparative Example 2 contains 97%, by weight of nonvolatilematerial, of an epoxy-acrylic dispersion. The epoxy-acrylic dispersioncontains 33% nonvolatile material, and is based on an advanced epoxyresin, styrene, ethyl acrylate, methyl methacrylate, and methacrylicacid. The epoxy-acrylic dispersion of Comparative Example 2 is preparedin an essentially identical manner as Example 2, except that sorbic acidis omitted and the epoxy resin used in Comparative Example 2 is advancedprior to the synthesis, rather than as a first step of the synthesis.The composition of Comparative Example 2 contains the same curing agentand lubricant, in the same amounts, as Example 1; and contains 30%nonvolatile material.

The compositions of Example 1 and Comparative Examples 1 and 2 wereapplied to a metal substrate (e.g., an aluminum substrate), and thencured to provide a coated metal substrate. The coated metal substratesthen were tested, comparatively, for use as the interior surface of afood or beverage container. As will be demonstrated more fullyhereinafter, a cured coating composition resulting from curing a coatingcomposition of the present invention is suitable as the interior orexterior coating of a metal container for food or beverages, or for aclosure.

In particular, a coating composition of the present invention is appliedto a metal substrate, then cured for a sufficient time at a sufficienttemperature, such as for about 3 to about 5 minutes at about 350° F. toabout 500° F., to provide an adherent cured coating composition on themetal substrate. The coated metal substrate then is shaped into acontainer or other metal article.

Therefore, the compositions of Example 1 and Comparative Examples 1 and2 were individually applied to a clean, untreated aluminum substrate ina sufficient amount to provide a cured film thickness of about 0.1 mil.Each composition was reduced to a solids content of about 28% by weightwith deionized water before applying the composition to the metalsubstrate. After individually applying a composition of Example 1 or acomposition of Comparative Examples 1 and 2 to an aluminum substrate,the composition was cured through an HVHT coil oven at 450° F. for about16 seconds. Each of the cured coating compositions had a smooth, glossyappearance and was defect free.

Table I summarizes the results of different tests performed on the curedcoating compositions. TABLE I

                  TABLE I    ______________________________________    Comparative Tests             Film    Pencil                 DOW    Composition             Weight.sup.1                     Hardness  WF.sup.2                                     WP(B,A).sup.3                                            (B/A)    ______________________________________    Example 1             7.3     2H-3H     0.3, 0.3                                     100/100                                            80/100    Comparative             7.3     2H-3H     0.3, 0.5                                     100/100                                            100/100    Ex. 2    Comparative             7.2     2H        0, 0  100/100                                            60/100    Ex. 1    (control)    ______________________________________     .sup.1 In milligrams per square inch of substrate;     .sup.2 A wet feathering (WF) test, the coated panels, after immersion in     150° F. water for 15 minutes, were tested for an ability to resist     forming torn or protruding edges when a tab of the coated metal substrate     is removed from the coated metal substrate, the test simulates removal of     a tab from an easyopen aluminum can, 0 (best results)    5 (worst     results);     .sup.3 B/A is blush/adhesion, 100excellent, 90good, 0total loss, Wp is we     pasteurization, the coated substrate is tested after immersion in     180° F. water for 30 minutes. Dow refers to a standard test wherei     the coated substrate is tested by immersing the coated aluminum substrate     in a boiling aqueous solution including 1 weight % Dowfax 2A1 (an anionic     surfactant) for 15 minutes, then testing for blush and adhesion.

The results summarized in Table I show that the composition of Example 1has a better blush resistance than a presently used commercialcomposition (Comparative Example 1).

The compositions of Example 1 and Comparative Example 2 also were testedfor process resistance. In these tests, liquids are placed in contactwith the coated substrate for a predetermined period of time underdifferent conditions, then the substrates are tested for resistance tothe effects of these various liquids in an enamel rating test.

The enamel rating tests the continuity of a cured coating film appliedto a can part, such as a can end or a can body. A can end or can body isformed after the metal substrate is coated. Therefore, the cured coatinghas been deformed during this manufacturing step. The data presented inTable II show that the enamel rating for a composition of the presentinvention (Example 1) is substantially better than the enamel rating ofComparative Example 2.

The enamel rating test measures the passage of current from an electrodethrough an electrolyte to the formed can part. The coating functions asan insulator, and, accordingly, no current flows if film continuity isperfect. The lower the milliamp reading, the more continuous the coatingon the metal substrate. The data in Table II shows a relatively lowmilliamp reading for can parts coated with the composition of Example 1,therefore, showing good film continuity. The composition of Example 1showed substantially better process resistance because of a betterenamel rating.

                  TABLE II    ______________________________________    Comparative Testing                              Comparative    Test.sup.1      Example 1 Example 2    ______________________________________    Coated substrate                    0.39 ± 0.29                              1.68 ± 0.91    (as made)    After 5 minutes in                    4.75 ± 1.76                              10.62 ± 2.61    boiling Dowfax 2A1    3 days @ 120° F.                    2.49 ± 1.25                              6.65 ± 2.16    Diet Coke    7 days @ 100° F.                    --        5.0 ± 2.53    Diet Coke    3 days @ 120° F.                    1.70 ± 0.97                              4.48 ± 1.43    Diet Sprite    ______________________________________     .sup.1 All tests are enamel ratings, in milliamps. Tests were performed     after subjecting a coated substrate to the indicated conditions.

In general, the composition of Example 1 demonstrates improvedflexibility, adhesion, and enamel rating over the composition ofComparative Example 2. Example 1 also exhibited properties comparable tothe presently used commercial vinyl organosol composition of ComparativeExample 1. In addition, the compositions of the present inventionexhibit an improved solids/viscosity relationship permitting theformulation of a high solids composition having an acceptable viscosityfor handling and application. The present coating compositions,therefore, have exhibited coating properties at least equal to currentcommercial compositions for similar end uses.

The data summarized in Tables I and II illustrate that a coatingcomposition of the present invention provides a cured coatingcomposition useful as the interior or exterior coating of a food orbeverage container, or a closure for a food product container. Thepresent compositions demonstrate excellent blush resistance andexcellent adhesion. The blush resistance test demonstrates the abilityof a cured coating to resist attack by a hot detergent solution andother liquids. A coating composition for a metal container mustdemonstrate excellent adhesion and flexibility because metal containersare manufactured by first coating flat sheets of the metal substrate,then forming the coated sheets into a desired shape. Coatings havingpoor adhesion properties can separate from the metal substrate duringthe shaping process. A lack of adhesion, therefore, can adversely affectthe ability of the cured coating composition to inhibit corrosion of themetal substrate. A present coating composition exhibits an excellentadhesion to a metal substrate, and, therefore, the coating compositioncan be applied to a metal substrate, cured, and the metal substratesubsequently can be deformed without adversely affecting continuity ofthe coating film.

The present coating compositions also provided a cured coatingcomposition having excellent flexibility. Flexibility is an importantproperty of a cured polymeric coating because the metal substrate iscoated prior to stamping or otherwise shaping the metal substrate into adesired metal article, such as a metal container. The coated metalsubstrate undergoes severe deformations during the shaping process, andif a coating lacks sufficient flexibility, the coating can form cracksor fractures. Such cracks result in corrosion of the metal substratebecause the aqueous contents of the container have greater access to themetal substrate. Metal substrates coated with a present coatingcomposition were deformed into the shape of a metal can. No cracks orfractures were observed. In addition, as previously described, a curedcoating provided by a coating composition of the present invention issufficiently adherent to the metal substrate, and remains sufficientlyadherent during processing into a metal article, and, therefore, furtherenhances corrosion inhibition.

The comparative tests illustrated in Tables I and II demonstrate that acured coating composition of the present invention maintains adhesion tothe metal substrate; is flexible; is sufficiently hard and, therefore,is scratch and mar resistant; resists blush; and resists chemicalattack.

As an added advantage, a composition of the present invention can becured over a relatively wide temperature range of about 350° F. to about500° F., and over relatively wide time period of about 3 minutes toabout 5 minutes, without adversely affecting the advantageous physicaland chemical properties of the cured coating composition. A containermanufacturer, therefore, does not have to design the coating processaround the curing characteristics of the coating composition; nor doesthe coating manufacturer have to tailor the curing characteristics ofthe coating composition to a particular coating process. The presentcoating composition, therefore, has a more universal range ofapplications. Furthermore, the wide curing range and the chemical andphysical properties demonstrated by the present coating compositionsmakes a waterborne coating composition useful for both the exterior andinterior of can bodies and can ends. Conventionally, different coatingcompositions are used for the can body and can end, and for the exteriorand interior of the container. This further expands the range ofapplications for the present composition.

Obviously, many modifications and variations of the invention ashereinbefore set forth can be made without departing from the spirit andscope thereof and, therefore, only such limitations should be imposed asare indicated by the appended claims.

What is claimed is:
 1. A water-dispersible polymer having the structure

    E--L--A,

wherein E is an epoxy portion of the polymer having at least one epoxygroup, A is a polymerized acrylic portion of the polymer, and L is alinking portion of the polymer which covalently links E to A, saidpolymer prepared from (a) an epoxy compound having about two epoxygroups; (b) a linking compound having(i) either conjugated carbon-carbondouble bonds or a carbon-carbon triple bond, and (ii) a moiety capableof reacting with an epoxy group, said linking compound present in anamount of about 0.003% to about 2.5% by weight of the polymer and in anamount sufficient to react with at least 1% and up to about 50% of theepoxy groups provided by the epoxy compound; and (c) acrylic monomers,at least a portion of which are selected from the group consisting of anα,β-unsaturated carboxylic acid, acrylamide methacrylamide and mixturesthereof, to render the polymer water dispersible; wherein the epoxygroup of epoxy portion E is opened with water, ammonia, a primary amine,a secondary amine, an alcohol, a diol, a phenol, an alkanolamine,phosphoric acid, a phosphoric acid monoester, a phosphoric acid diester,or a mixture thereof.
 2. The polymer of claim 1 comprising about 5% toabout 95% by weight of the epoxy portion E.
 3. The polymer of claim 1wherein the epoxy compound has an epoxy equivalent weight of about 180to about 20,000.
 4. The polymer of claim 1 wherein the epoxy compoundcomprises a polyether diepoxide prepared in a reaction between abisphenol and a compound having about two epoxy groups.
 5. The polymerof claim 1 wherein the linking compound contains conjugatedcarbon-carbon double bonds.
 6. The polymer of claim 1 wherein thelinking compound contains a carbon-carbon triple bond.
 7. The polymer ofclaim 1 wherein the linking compound has the structure ##STR13## whereinR₁ is selected from the group consisting of hydrogen, phenyl, C₁ -C₁₀alkoxy-substituted phenyl, halo-substituted phenyl, C₁ -C₁₈alkyl-substituted phenyl, C₁ -C₁₈ alkyl, C₅ -C₇ cycloalkyl,phenyl-substituted C₁ -C₁₈ alkyl, phenyl-substituted C₅ -C₇ cycloalkyl,halo-substituted C₁ -C₁₈ alkyl, halo-substituted C₅ -C₇ cycloalkyl,unsaturated C₁ -C₁₈ aliphatic hydrocarbyl, and unsaturated C₅ -C₇cycloaliphatic hydrocarbyl; r is a numeral from 1 to 6; s is a numeralfrom 0 to 6; p is a numeral from 0 to 18; and Y is a moiety capable ofreacting with an epoxy group.
 8. The polymer of claim 7 wherein the Ygroup is selected from the group consisting of a carboxylic acid group;a hydroxyl group; an amino group --N(R₂)₂ ; an amido group --CON(R₂)₂,wherein R₂, independently, are hydrogen, C₁ -C₄ alkyl, or phenyl; and amercapto group --SR₃, wherein R₃ is hydrogen, C₁ -C₄ alkyl, or phenyl.9. The polymer of claim 1 wherein the linking compound is selected fromthe group consisting of sorbic acid, sorbic alcohol, a dicyclopentadieneacids, a conjugated unsaturated fatty acid, eleostearic acid,3-pentyn-1-ol, 2-pentyn-1-ol, 4-pentynoic acid, 4-pentyn-1-ol,4-pentyn-2-ol, 1-pentyn-3-ol, heptacose-10,12-diynoic acid,heptadeca-2,4-diynoic acid, heneicosa-2,4-diynoic acid, 2-heptynoicacid, 2-hexynoic acid, nonacosa-10,12-diynoic acid, nonadeca-1,4-diynoicacid, 2-nonynoic acid, pentadeca-2,4-diynoic acid,pentacosa-10,12-diynoic acid, phenyl-propiolic acid, propiolic acid,tetrolic acid, tricosa-10,12-diynoic acid, 10-undecynoic acid,1-butyn-3-ol, 2-butyn-1-ol, 3-butyn-1-ol, 2-decyn-1-ol, 3-decyn-1-ol,3,6-dimethyl-1-heptyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol,3,4-dimethyl-1-pentyn-3-ol, 3-ethyl-1-heptyn-3-ol, 4-ethyl-1-hexyn-3-ol,3-ethyl-5-methyl-1-heptyn-3-ol, 4-ethyl-1-octyn-3-ol,3-ethyl-1-pentyn-3-ol, 1-ethynyl-1-cyclohexanol, 1-heptyn-3-ol,2-heptyn-1-ol, 3-heptyn-1-ol, 4-heptyn-2-ol, 5-heptyn-3-ol,1-hexyn-3-ol, 2-hexyn-1-ol, 3-hexyn-1-ol, 4-hexyn-2-ol, 5-hexyn-1-ol,5-hexyn-3-ol, 3-methyl-1-butyn-3-ol, 5-methyl-1-hexyn-3-ol,3-methyl-1-pentyn-3-ol, 3-nonyn-1-ol, 1-octyn-3-ol, 3-octyn-1-ol,1-phenyl-2-propyn-1-ol, 2-propyn-1-ol, 10-undecyn-1-ol,3-aminophenyl-acetylene, propargylamine, and mixtures thereof.
 10. Thepolymer of claim 1 wherein the linking compound has a maximum of twelvecarbon atoms.
 11. The polymer of claim 1 wherein the polymerized acrylicportion A comprises at least 5%, by weight, of monomers capable ofrendering the polymer water dispersible.
 12. The polymer of claim 1comprising about 0.25% to about 20%, by weight of the polymer, ofmonomers capable of rendering the polymer water dispersible.
 13. Thepolymer of claim 1 wherein the α,β-unsaturated carboxylic acid isselected from the group consisting of acrylic acid, methacrylic acid,crotonic acid, itaconic acid, maleic acid, mesaconic acid, citraconicacid, sorbic acid, fumaric acid, and mixtures thereof.
 14. The polymerof claim 1 wherein the polymerized acrylic portion A comprises 0% toabout 95% of a vinyl monomer, an ester of an α,β-unsaturated acid, anacrylonitrile, or a mixture thereof.
 15. The polymer of claim 14 whereinthe polymerized acrylic portion A comprises a monomer selected from thegroup consisting of styrene; a halostyrene; isoprene; a conjugatedbutadiene; α-methylstyrene; vinyl toluene; vinyl naphthalene; methylacrylate; ethyl acrylate; propyl acrylate; isopropyl acrylate; butylacrylate; isobutyl acrylate; pentyl acrylate; isoamyl acrylate; hexylacrylate; ethylhexyl acrylate; lauryl acrylate; a C₄ -C₁₂ alkylacrylate; a C₁ -C₁₂ alkyl methacrylate; a C₁ -C₁₂ alkyl crotonate;dimethyl maleate; dibutyl fumarate; vinyl chloride; acrylonitrile;methacrylonitrile; vinyl acetate; vinyl propionate; vinyl stearate; andmixtures thereof.
 16. The polymer of claim 1 wherein the epoxy portion Ehas the structure ##STR14## wherein t is 0 to about 70; the linkingportion L comprises sorbic acid; and the polymerized acrylic portion Ais predominantly acrylic acid, methacrylic acid, or a mixture thereof.17. The polymer of claim 16 wherein the polymerized acrylic portion Afurther comprises a monomer selected from the group consisting ofstyrene, methyl acrylate, ethyl acrylate, butyl acrylate, methylmethacrylate, and mixtures thereof.
 18. A water-dispersible polymerprepared by a method comprising:(a) reacting (i) an epoxy compoundhaving about two epoxy groups with (ii) a sufficient amount of a linkingcompound to consume at least 1% and up to about 50% of epoxy groupsprovided by the epoxy compound, said linking compound present in anamount of about 0.003% to about 2.5% by weight of the polymer, andhaving(A) either conjugated carbon-carbon double bonds or acarbon-carbon triple bond, and (B) a moiety capable of reacting with anepoxy group, to provide a modified epoxy compound having at least oneepoxy group and wherein the linking compound is covalently bonded to theepoxy compound; (b) hydrolyzing the epoxy group of the modified epoxycompound of step (a) to provide an α-glycol at a terminal end of themodified epoxy compound; and (c) reacting the hydrolyzed epoxy compoundof step (b) with (iii) a sufficient amount of acrylic monomer selectedfrom the group consisting of an α,β-unsaturated carboxylic acid,acrylamide, methacrylamide and mixtures thereof, such that the acrylicmonomer copolymerizes with the conjugated carbon-carbon double bonds orthe carbon-carbon triple bond of the linking compound to provide thewater-dispersible polymer.
 19. The water-dispersible polymer of claim 18wherein step (b) of the method comprises ring opening the epoxy group ofthe modified epoxy compound after step (a) with a nitrogen compoundhaving the structure (R₄)₂ NH, wherein the R₄ groups are, independently,hydrogen, an alkyl group having one to six carbon atoms, phenyl, or ahydroxyalkyl group having one to six carbon atoms, to provide anα-aminoalcohol at a terminal end of the modified epoxy compound.
 20. Thewater-dispersible polymer of claim 18 wherein step (b) of the methodcomprises ring opening the epoxy group of the modified epoxy compoundafter step (a) with a hydroxyl-containing compound having the structureR₅ OH, wherein the R₅ group is hydrogen, an alkyl group having one tosix carbon atoms, phenyl, or a hydroxyalkyl group having one to sixcarbon atoms, to provide an α-hydroxy ether at a terminal end of themodified epoxy compound.
 21. The water-dispersible polymer of claim 18wherein step (b) of the method comprises ring opening the epoxy group ofthe modified epoxy compound after step (a) with a phosphoric acid havingthe structure ##STR15## wherein the R₆ groups are, independently,hydrogen, an alkyl group having one to six carbon atoms, or phenyl, toprovide an α-hydroxy phosphate ester at a terminal end of the modifiedepoxy compound.
 22. A coating composition comprising:(a) about 5% toabout 60%, by weight of non-volatile material, of a water-dispersiblepolymer having the structure

    E---L--A,

wherein E is an epoxy portion of the polymer, said epoxy portion Ederived from an epoxy compound having about two epoxy groups; L is alinking portion of the polymer, said linking portion L derived from alinking compound having (A) either conjugated carbon-carbon double bondsor a carbon-carbon triple bond, and (B) a moiety capable of reactingwith an epoxy group, said linking compound present in an amount of about0.003% to about 2.5% by weight of the polymer and in an amountsufficient to react with at least 1% and up to about 50% of epoxy groupsprovided by the epoxy compound; and A is a polymerized acrylic portionof the polymer, said acrylic portion A comprising polymerized acrylicmonomers, at least a portion of said monomers selected from the groupconsisting of an α,β-unsaturated carboxylic acid, acrylamide, andmethacrylamide, to render the polymer water dispersible, wherein theepoxy portion E of the polymer is covalently linked to the acrylicportion A by the linking portion L and wherein the epoxy group of epoxyportion E is opened with water, ammonia, a primary amine, a secondaryamine, an alcohol, a diol, a phenol, an alkanolamine, phosphoric acid, aphosphoric acid monoester, a phosphoric acid diester, or a mixturethereof; (b) a sufficient amount of a fugitive base to disperse thewater-dispersible polymer in water; (c) about 0.5% to about 25%, byweight of nonvolatile material, or a curing agent; and (d) a carriercomprising water and a volatile organic solvent.
 23. The composition ofclaim 22 wherein the polymerized acrylic portion A comprises anα,β-unsaturated acid, and wherein a sufficient amount of the fugitivebase is present to neutralize about 20% to about 100% of carboxylic acidgroups present in the acrylic portion A of the polymer.
 24. Thecomposition of claim 22 wherein the fugitive base is selected from thegroup consisting of a primary amine, a secondary amine, a tertiaryamine, a primary alkanolamine, a secondary alkanolamine, a tertiaryalkanolamine, ammonium hydroxide, an alkylammonium hydroxide, andmixtures thereof, wherein the alkyl groups of the amines, alkanolaminesand alkylammonium hydroxides have one to about four carbon atoms. 25.The composition of claim 22 wherein the fugitive base is selected fromthe group consisting of ammonium hydroxide, a tetraalkylammoniumhydroxide wherein an alkyl group has one to about 4 carbon atoms,tetramethylammonium hydroxide, monoethanolamine, dimethylamine,methyldiethanolamine, benzylamine, diisopropylamine, methylethanolamine,butylamine, piperazine, dimethylethanolamine, diethylethanolamine,diethanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine,triethylamine, 2-dimethylamine-2-methyl-1-propanol, diisopropanolamine,trimethylamine, N-methylpiperidine, 2-amino-2-methyl-1-propanol,piperidine, pyridine, dimethylaniline, and mixtures thereof.
 26. Thecomposition of claim 22 wherein the curing agent is selected from thegroup consisting of a phenolic resin, an aminoplast, a carbodiimide, andmixtures thereof.
 27. A method of coating a metal substratecomprising:(i) applying a coating composition of claim 22 to at leastone surface of the metal substrate; and (ii) heating the metal substratehaving the coating composition applied thereon for a sufficient time andat a sufficient temperature to remove the fugitive base and the carrierfrom the composition and provide a crosslinked cured coatingcomposition.
 28. The method of claim 27 wherein the metal substratehaving the coating composition applied thereon is heated for about 6seconds to about 15 minutes at a temperature of about 350° F. to about500° F.
 29. A metal article having at least one surface thereof coatedwith an adherent layer of a cured coating composition of claim
 22. 30.The polymer of claim 1 wherein the linking compound L is sorbic acid,and the polymerized acrylic portion A is prepared from acrylic monomersselected from the group consisting of acrylic acid, methacrylic acid,styrene, ethyl acrylate, and methyl methacrylate.